m (grammatical edits, punctuation edits) |
|||
Line 9: | Line 9: | ||
You can enter an LTL formula in the dialog's text field. | You can enter an LTL formula in the dialog's text field. | ||
We explain the supported syntax below. | We explain the supported syntax below. | ||
If the model checker finds a counter-example the animator navigates to the last state of the counter-example. The full path can then be seen in the history. | If the model checker finds a counter-example, the animator navigates to the last state of the counter-example. The full path can then be seen in the history. | ||
=== Search options === | === Search options === | ||
The model checker searches for a counter-example (i.e. a path that does not satisfy the current formula). Where the checked | The model checker searches for a counter-example (i.e. a path that does not satisfy the current formula). Where the checked paths through the model's search space start depend on the following options: | ||
# '''Start search in initialisation'''<br>All | # '''Start search in initialisation'''<br>All paths that start in a state of the initialisation of the machine are checked. | ||
# '''Start search in current state'''<br>All | # '''Start search in current state'''<br>All paths that start in the current state are checked. | ||
# '''Start in initialisation, but check formula in current state''' <br>All | # '''Start in initialisation, but check formula in current state''' <br>All paths that start in a state of the initialisation of the machine are checked, but the formula is mapped to the current state. For example, this option can be used to check properties like "Is this state only reachable directly after executing operation `xy`?": The formula would be `Y[xy]`. This is equivalent to "G (current => f)" with f as the entered formula and using the option "Start search in initialisation". | ||
Note: Whereas `Y true` is always false when checked with option 1 or 2, it is usually true (but not in all cases) for option 3. | Note: Whereas `Y true` is always false when checked with option 1 or 2, it is usually true (but not in all cases) for option 3. | ||
Line 22: | Line 22: | ||
=== Search results === | === Search results === | ||
There are three possible results: | There are three possible results: | ||
* The formula is true for all valid | * The formula is true for all valid paths. | ||
* There is a path that does not satisfy the formula. This counter-example is shown in the history of the animator. | * There is a path that does not satisfy the formula. This counter-example is shown in the history of the animator. | ||
* No counter-example was found, but the absence of a path that does not satisfy the formula can not be guaranteed because the state space was not fully explored. | * No counter-example was found, but the absence of a path that does not satisfy the formula can not be guaranteed because the state space was not fully explored. | ||
Line 43: | Line 43: | ||
** Whether a state is a deadlock state can be checked with `deadlock`. | ** Whether a state is a deadlock state can be checked with `deadlock`. | ||
* Transition propositions:<br>If the next executed operation in the path is `Op`, the expression `[Op]` can be used. Also patter-matching for the arguments of the operation is supported. E.g. `[Op(3,,4*v)]` checks if the next operation is `Op` and that the first argument is 3 and the third argument is `4*v` where `v` is a variable of the machine. <br> Arbitrary B expressions can be used as patterns. Constants and variables of the machine can be used | * Transition propositions:<br>If the next executed operation in the path is `Op`, the expression `[Op]` can be used. Also patter-matching for the arguments of the operation is supported. E.g. `[Op(3,,4*v)]` checks if the next operation is `Op` and that the first argument is 3 and the third argument is `4*v` where `v` is a variable of the machine. <br> Arbitrary B expressions can be used as patterns. Constants and variables of the machine can be used. Variables have the values of the state where the operations starts. | ||
* Logical operators | * Logical operators | ||
Line 69: | Line 69: | ||
LTL formulas can be stored in the `DEFINITIONS` section of a B machine. | LTL formulas can be stored in the `DEFINITIONS` section of a B machine. | ||
The name of the definition must start with `ASSERT_LTL` and a string must | The name of the definition must start with `ASSERT_LTL` and a string must | ||
be specified. | be specified. For example: | ||
DEFINITIONS | DEFINITIONS | ||
ASSERT_LTL == "G ([add] => X {card(db)>0})" | ASSERT_LTL == "G ([add] => X {card(db)>0})" | ||
All assertions can be checked automatically by selecting "Check LTL assertions" in the "Verify" menu. Each formula is checked for all paths starting in the states of the | All assertions can be checked automatically by selecting "Check LTL assertions" in the "Verify" menu. Each formula is checked for all paths starting in the states of the initialization of the machine. | ||
Formulas that pass are marked green, formulas that failed are marked red. | Formulas that pass are marked green, formulas that have failed are marked red. | ||
[[File:ltlassertions.png]] | [[File:ltlassertions.png]] | ||
Line 80: | Line 80: | ||
With the command line version of ProB it is possible to check several LTL formulas with one call. The command has the following syntax | With the command line version of ProB it is possible to check several LTL formulas with one call. The command has the following syntax | ||
probcli -ltlfile FILE ... | probcli -ltlfile FILE ... | ||
The file FILE contains one or more sections | The file FILE contains one or more sections where each section has the form | ||
[Name] | [Name] | ||
Formula | Formula |
ProB provides support for LTL (linear temporal logic) model checking. For an introduction see the Wikipedia Article.
To use this feature, select "Check LTL formula..." in the "Verify" menu. The following dialog appears:
You can enter an LTL formula in the dialog's text field. We explain the supported syntax below. If the model checker finds a counter-example, the animator navigates to the last state of the counter-example. The full path can then be seen in the history.
The model checker searches for a counter-example (i.e. a path that does not satisfy the current formula). Where the checked paths through the model's search space start depend on the following options:
Note: Whereas `Y true` is always false when checked with option 1 or 2, it is usually true (but not in all cases) for option 3.
There are three possible results:
The LTL model checker searches in the already explored search space of the model. If a state is encountered that has not been explored before, the state will be explored (i.e. all transitions to successor states are calculated). The number of how often this can happen is limited by the field "Max no. of new states".
Depending on the LTL formula, a partially explored state space can be sufficient to find a counter-example or to assure the absence of a counter-example. If there's still the possibility of a counter-example in the remaining unexplored state space, the user will get a message.
ProB supports LTLe, an extended version of LTL. In contrast to standard LTL, LTLe also supports propositions on transitions, not only on states. In practice, this allows the operator `[...]` (see below). Also Past-LTL is supported.
LTL formulas can be stored in the `DEFINITIONS` section of a B machine. The name of the definition must start with `ASSERT_LTL` and a string must be specified. For example:
DEFINITIONS ASSERT_LTL == "G ([add] => X {card(db)>0})"
All assertions can be checked automatically by selecting "Check LTL assertions" in the "Verify" menu. Each formula is checked for all paths starting in the states of the initialization of the machine. Formulas that pass are marked green, formulas that have failed are marked red.
With the command line version of ProB it is possible to check several LTL formulas with one call. The command has the following syntax
probcli -ltlfile FILE ...
The file FILE contains one or more sections where each section has the form
[Name] Formula
The formula itself can spread several lines. Additional comments can be added with a leading #.
If a counter-example is found, the trace of the counter-example is saved into the file ltlce_Name.trace, where Name is the name of the formula in the LTL file.